Query Modifiers

Query Modifiers are used for retrieving data that has been stored in the archive. They are used along with sampling and calculation modes to get a specific set of data.

  • The time interval is great than 1 minute.
  • The collection interval is greater than 1 second.
  • The data node size is greater than the default 1400 bytes.
  • The data type of the tags is String or Blob.

Query performance varies depending on all of the above factors.

Use this query modifier only with FirstRawValue, FirstRawTime, LastRawValue, and LastRawTime calculation modes.

EXCLUDESTALE:
  • Stale tags are tags that have no new data samples within a specified period of time, and which have the potential to add to system overhead and slow down user queries.
  • The EXCLUDESTALE query modifier allows for exclusion of stale tags in data queries.
  • Unless permanently deleted, stale tags from the archiver are not removed but are simply marked as stale. Use the query without this query modifier to retrieve the sample values.
  • Data is not returned for stale tags. An ihSTATUS_STALED_TAG error is returned instead.